This invention relates to a method and system of controlling an injection molding machine, and more particularly to a method and system of automatically controlling an injection condition at the time of pouring molten metal into a metal mold of such an injection molding machine as a die cast machine or the like for the purpose of always obtaining cast products having uniform and excellent quality.
In order to obtain cast products of uniform quality with an injection molding machine, for example, a die cast machine, it is essential to adequately set injection conditions such as the injection speed of the injection molding machine. Accordingly, in prior art injection molding machines, the operator determines the injection speed by relying upon measuring instruments or his feeling and manually adjusts the degree of opening of an injection valve so as to make it correspond to the injection speed thus determined. More particularly, according to the prior art method, the degree of opening of the injection valve is set to a predetermined value such that the low injection speed, high injection speed and pressure build-up time will not vary so as to stabilize the injection or molding conditions. However, the nonuniformities of the low injection speed, high injection speed and pressure build-up time are caused by variations in the molten metal temperature, metal mold temperature, operating oil temperature, accumulator pressure, etc. so that it has been difficult to always obtain molded or cast products of excellent quality. Although it has been tried to maintain these variable factors at constant values, such efforts have failed because it has been difficult to control these factors at a high response speed.
We have found that these difficulties can be overcome by noting the fact that molding or injection conditions necessary to obtain satisfactory products involve factors relating to the product including its thickness, weight, material, configuration, and field of application; factors relating to the mold including thickness of the stationary mold, the length of a sprue, gate area, mold temperature, injection cylinder diameter, etc.; machine factor regarding stroke, amount of projection, accumulator pressure; and other factors including cooling water temperature, operating oil temperature, mold release agent, etc. By using all of these factors for setting the injection condition, by constantly supervising or measuring specific factors that vary during the injection operation and by calculating an optimum injection condition based on data regarding these variable factors, the injection condition can be automatically adjusted to an optimum condition.
Among the variable factors that determine the injection condition, the product factor becomes a fixed factor by specifying the product. Then the variable factors are represented by the molten metal temperature, accumulator pressure, metal mold temperature, and operating oil temperature. Accordingly, an optimum injection condition can readily be set by constantly supervising at least these varying factors and by inputting data thereof into a computer.